The present invention relates to a cleaning device and an image forming apparatus. In particular, the present invention is applicable to a cleaning device provided in an image forming apparatus such as a laser printer, a copying machine, facsimile machine, and multi-function machine of these apparatuses.
An image forming apparatus is provided with a cleaning device for collecting toner remaining on the surface of a photoconductor (e.g., photoconductor drum or photoconductor belt) or an intermediate transfer member (e.g., intermediate transfer belt or intermediate transfer drum) as image bearing bodies after transfer of a toner image.
As shown in FIG. 18, a cleaning device is known that comprises: a cleaning brush 2 rotating with contacting to an image bearing body 1, a collection roller 3 rotating with contacting to the cleaning brush 2, and a scraper 4 being fixed and contacting to the collection roller 3. The cleaning brush 2 is provided with a large number of hairs or brush fibers 2b implanted in an outer periphery of a core metal 2a. Toner 5 on a surface of the image bearing body 1 is mechanically scraped by the brush fibers 2b of the cleaning brush 2. A bias voltage of a polarity reverse to a charging polarity for the toner 5 is applied to the cleaning brush 2. For example, when a normal charging polarity of the toner 5 is negative, the bias voltage of positive polarity is applied to the cleaning brush 2. This bias voltage generates an electric field between the cleaning brush 2 and the image bearing body 1, so that the toner 5 is electrostatically adsorbed to the cleaning brush 2. The toner 5 collected by the cleaning brush 2 moves to the collection roller 3 owing to a potential difference between the cleaning brush 2 and the collection roller 3. The toner 5 on the surface of the collection roller 3 is mechanically scraped by the scraper 4.
A rotational direction (arrow A1) of the collection roller 3 and a rotational direction (arrow A2) of the cleaning brush 2 are set so that the collection roller 3 and the cleaning brush 2 move in the reverse directions to each other at a contact area between them. In FIG. 18, both of the collection roller 3 and the cleaning brush 2 rotates in the counterclockwise direction, so that they move in the reverse directions to each other at the contact area. In the following description, when a member rotates such that the member moves in a reverse direction relative to a reference member at a contact area between them, the rotational direction is referred to as a “reverse direction.” The rotation of the cleaning brush 2 (arrow A2) is in the reverse direction relative to the revolution of the image bearing body 1 (arrow A3). U.S. Pat. No. 5,600,405 discloses this type of cleaning device.
Each brush fiber 2b of the cleaning brush 2 receives forces in the same direction at the contact area between the cleaning brush 2 and the image bearing body 1 and at the contact area between the cleaning brush 2 and the collection roller 3. Thus, in a latter portion of the brush life, the brush fibers 2b curl or incline, causing decrease of the outer diameter of the cleaning brush 2 as shown in FIG. 19. This reduces the amount of nip of the cleaning brush 2 against the image bearing body 1 and the collection roller 3, and thereby reduces a cleaning performance. Further, even in the state that an operation of the cleaning brush 2 is stopped, the cleaning brush 2 keeps contacting with the image bearing body 1 and the collection roller 3. Thus, when a period during which the cleaning brush 2 is stopped continues for a prolonged time, the brush fibers 2b of the cleaning brush 2 incline permanently in the portions contacting with the image bearing body 1 and the collection roller 3 in the state of stop of the operation, as shown in FIG. 20. This reduces the cleaning performance.
Another cleaning device is known in which the rotational direction of the collection roller 3 is different from that of FIG. 18. Referring to FIG. 21, the rotational direction of the collection roller 3 (arrow A4) and the rotational direction of the cleaning brush 2 (arrow A2) are set so that the collection roller 3 and the cleaning brush 2 move in the same direction with each other at the contact area between them. In FIG. 21, the collection roller 3 rotates in a clockwise direction, while the cleaning brush 2 rotates in a counterclockwise direction, so that they move in the same direction with each other at the contact area between them. In the following description, when a member rotates such that the member moves in the same direction relative to a reference member at a contact area between them, the rotational direction of is referred to as “forward direction.” U.S. Pat. No. 5,561,513, Japan Patent Publication H06-70730, and U.S. Pat. No. 4,912,516 disclose this type of cleaning device. Of these documents, U.S. Pat. No. 5,561,513 discloses that in order to raise inclined brush fibers, a collection roller rotates in the forward direction relative to a cleaning brush, and that a circumferential speed ratio of the collection roller to the cleaning brush is set to be equal to or larger than three. However, when the circumferential speed ratio is set to be equal to or larger than three, a tip of a scraper wears rapidly. This reduces the efficiency of the scraper mechanically removing the toner from the collection roller.
As shown in FIG. 22, a cleaning device is also known that is provided with a pair of collection rollers 3A and 3B and a pair of corresponding scrapers 4A and 4B so as to improve the cleaning performance. One collection roller 3A rotates in the reverse direction relative to a cleaning brush 2 as indicated by an arrow A5, while the other collection roller 3B rotates in the forward direction relative to the cleaning brush 2 as indicated by an arrow A6. Japan Patent Publication H02-4911 discloses this type of cleaning device. However, this approach causes a complexity and a size increase in the device, and hence raises the cost.
As described above, the conventional cleaning devices can not achieve efficient removal of the toner from the image bearing body, prevention of permanent inclination and wear in the brush fibers of the cleaning brush, and a simple configuration.
Further, since the toner is removed mechanically by the cleaning brush, the collection roller, and the scraper, the toner is pulverized and scattered during the cleaning operation in the cleaning device. The pulverized toner accumulates on the surfaces of the image bearing body, the cleaning brush, and the collection roller after the stop of cleaning operation. Thus, when the cleaning device is restarted, the cleaning performance is degraded at an early stage, so that the toner remains on the surface of the image bearing body. The remnant toner causes image noise.